An intake manifold for an engine can have a molded integral one-piece construction. It can be desirable for such an intake manifold to include coiled runners which are arranged side-by-side and oppositely curved so that a generally cylindrical plenum is defined by the space around which the runners are coiled. When molding such an intake manifold, it can be difficult to form the runner inlets with flared edges and to form the outer longitudinal edges of the runners, which adjoin the plenum, in a rounded shape. It is a well-known advantage for air inlets of intake manifolds to have a "bell-mouth" or flared entrance. This converging nozzle principle enhances the flow of air into any tube end.
It is known to form plastic intake manifolds for V-type engines by using a "lost core" molding process wherein the plastic manifold is formed around multiple cores which are subsequently melted within the intake manifold and drained from it. A separate plastic "bellmouth" (i.e., a runner inlet which is outwardly flared) is attached by snaps and/or glue to the entrance of each individual runner. Such a manifold can require a plenum having a substantial size to enable attachment of the "bellmouths" to the runners. The size of such a plenum typically must be reduced by inserting a displacement member or mechanism therein. This can result in increased complexity and cost of the intake manifold and the method of making it, and in reduced durability of the intake manifold.